The purpose of this project is to reveal the mechanisms of bactericide uptake and transport in citrus plant and establish a theoretical basis for developing technologies to improve the efficacy of bactericides, which is helpful to provide potential solution to the development of effective chemotherapeutic tools for HLB management. Achieving this outcome will require progress in the following three tasks: (1) to compare the delivery efficacy of bactericides with three application methods (foliar spraying, truck injection, and root administration) based on the uptake and dynamic movement/distribution of the bactericide within the tree; (2) to clarify the systemic movement and transportation mechanisms of bactericides within the phloem of tree; and (3) to investigate the effects of citrus variety and age on the delivery efficacy of bactericides. This project requires a combination of greenhouse studies and field trials. Prior to conducting these experiments, a sensitive and accurate quantifying method of bactericides (oxytetracycline and streptomycin) in citrus tissues is needed. This project officially started on December 1, 2018. This is the 6th quarterly progress report covering March/01 to May/31, 2020. During this period, all the faculty/staffs/graduate students at the University of Florida were required to work at home without accessing the laboratory due to COVID-19 pandemic. Therefore, we have conducted and/or completed only a part of the planned work/research tasks:1. Preparation for field trials including: 1) purchase of equipment and chemicals, 2) creation of questionaires for field survey to the citrus growers, and 3) selection of field sites.2. Performance of literrature review related to this study. The work planned for the next quarter: The major goals of research for the next three months are to analyze the data and evaluate the delivery efficacy of three different application methods for bactericides in greenhouse experiments. Based on the above results, field experiments will be started and the following research tasks will be performed during the next quarter (June 1, 2020 to August 31, 2020):1) collection and analysis of the obtained data from greenhouse experiments; 2) implementation of field experiments; 3) conducting foliar spraying experiments in the field sites; 4) preparation of trunk injection treatments for the field experiments; and 5) preparation of the next quarterly progress report.